purge function

Implementation

Future purge(Connection conn,
    Map<String, Map<String, SqlType>> tables,
    Map<String, IndexInfo> indexes, Map<String, RuleInfo> rules) {

  return Future.forEach(rules.keys,
    (name) => conn.execute('drop rule "$name" on "${rules[name]!.table}"')
    .catchError((ex) {}, test: _isUndefined))
  .then((_) => Future.forEach(indexes.keys.toList().reversed,
    (name) => conn.execute('drop index "$name"')
    .catchError((ex) {}, test: _isUndefined)))
  .then((_) {
    final tblsGened = HashSet<String>();
    final refsDeferred = <_DeferredRef>[];
    for (final otype in tables.keys)
      _scanDeferredRefs(otype, tables[otype]!, tblsGened, refsDeferred);
    return Future.forEach(refsDeferred,
        (_DeferredRef defRef) => defRef.drop(conn)
        .catchError((ex) {}, test: _isUndefined));
  })
  .then((_) => Future.forEach(
    tables.keys.toList().reversed,
    (String name) => conn.execute('drop table "$name"')
    .catchError((ex) {}, test: _isUndefined)
  ));
}